A disc brake system includes opposing brake pads that axe moved towards one another and into engagement with a brake rotor to create a clamp force to slow or stop a moving vehicle. A drum brake system includes opposing brake shoes that are moved away from one another and into engagement with a brake drum to create a clamp force to slow or stop a moving vehicle.
Both disc brake systems and drum brake systems typically include a parking brake system that functions to move the brake pads or brake shoes, respectively, into engagement with the respective brake rotor or brake drum to create a clamp force to maintain the vehicle in a stopped or parked position.
Some parking brake systems, brake systems, or both include a motor gear unit (MGU) and at least one rotary to linear stage mechanism. In disc brake systems, the MGU and the rotary to linear stage cooperate to move the brake pads into engagement with the brake rotor to create the clamp force to maintain the vehicle in a stopped or parked position. In drum brake systems, the MGU and the rotary to linear stage mechanism cooperate to move the brake shoes into engagement with the brake drum to create the clamp force to maintain the vehicle in a stopped or parked position.
In some parking brake systems, brake systems, or both, the rotary to linear stage mechanism is a high efficiency mechanism. Efficiency may refer to how well, or how ‘efficiently” the mechanism converts or transfers torque from a motor or MGU into a linear load or output force. High efficiency rotary to linear stage mechanisms may be used to develop the clamp force faster while also reducing packaging space, weight, and cost of the system. However, after the clamp force is developed and the MGU is turned OFF, a high efficiency rotary to linear stage mechanism may back drive, which may result in an unintended reduction or elimination of clamp force, which may undesirably result in the vehicle rolling away.
Therefore, “self-locking” features have been proposed and incorporated into some brake systems to prevent back driving of high efficiency rotary to linear stage mechanisms after the clamp force is developed and the MGU is turned OFF. For example, various “non-back-drivable” elements such as worm type reduction gears and/or short pitch drive screws have been contemplated that incorporate friction to maintain the clamp force and prevent back driving. However, overcoming the friction of these self-locking features during a parking brake apply requires a bigger motor, which undesirably increases packing space, weight, and cost of the system.
Accordingly, a need exists for continued improvement. For example, it may be desirable to have a torque locking mechanism that maintains clamp force and prevents back driving of a brake system after electrical power to a motor of MGU is turned OFF. It may be desirable to have a torque locking mechanism that functions to prevent back driving of one or more rotary to linear stage mechanisms after the motor or MGU is turned OFF to prevent the clamp force from being prematurely reduced or eliminated. It may be desirable to have a torque locking mechanism that, during a parking brake apply, provides little to no friction or torque so that the clamp force can be developed quickly and efficiency, and after the parking brake apply is complete and the MGU is turned OFF, provides sufficient friction or torque to maintain the clamp force and prevent back driving of the system.